Marked increases in mucociliary clearance produced by synergistic secretory agonists or inhibition of the epithelial sodium channel.

Nam Soo Joo,Jin Hyeok Jeong,Jeffrey J Wine,Hyung-Ju Cho

doi:10.1038/srep36806

Nam Soo Joo, Jin Hyeok Jeong + Show 2 more

Open Access

https://doi.org/10.1038/srep36806

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Abstract

Mucociliary clearance (MCC) is a critical host innate defense mechanism in airways, and it is impaired in cystic fibrosis (CF) and other obstructive lung diseases. Epithelial fluid secretion and absorption modify MCC velocity (MCCV). We tested the hypotheses that inhibiting fluid absorption accelerates MCCV, whereas inhibiting fluid secretion decelerates it. In airways, ENaC is mainly responsible for fluid absorption, while anion channels, including CFTR and Ca2+-activated chloride channels mediate anion/fluid secretion. MCCV was increased by the cAMP-elevating agonists, forskolin or isoproterenol (10 μM) and by the Ca2+-elevating agonist, carbachol (0.3 μM). The CFTR-selective inhibitor, CFTRinh-172, modestly reduced MCCV-increases induced by forskolin or isoproterenol but not increases induced by carbachol. The ENaC inhibitor benzamil increased basal MCCV as well as MCCV increases produced by forskolin or carbachol. MCC velocity was most dramatically accelerated by the synergistic combination of forskolin and carbachol, which produced near-maximal clearance rates regardless of prior treatment with CFTR or ENaC inhibitors. In CF airways, where CFTR-mediated secretion (and possibly synergistic MCC) is lost, ENaC inhibition via exogenous agents may provide therapeutic benefit, as has long been proposed.

Highlights

mucociliary clearance velocity (MCCV) of isolated ferret tracheas was accelerated by treatments expected to increase fluid secretion or decrease fluid absorption
The results suggest that MCCV will be reduced in CF, and support the long-standing proposal that inhibiting ENaC should be beneficial in CF—this does not require that ENaC be upregulated in CF
The synergism observed by adding such a small amount of carbachol was unexpected

Summary

Methods

Mustela Putorius ferret tracheas of 6~36 months old were obtained 1–2 hr postmortem by pentobarbital sodium injection after acute experiments unrelated to our present study. Methods for ferret tissues were carried out in accordance with approved guidelines. Harvested tissues were placed in cold PhysioSolTM (Hospira, IL) for transport to the laboratory and transferred to ice-cold Krebs Ringer bicarbonate (KRB) buffer gassed with 95% O2 and 5% CO2 until the mucociliary clearance assays. The Krebs buffer contained 1.0 μM indomethacin to minimize endogenously generated prostaglandins during tissue preparation. Tracheas with intact cartilage were dissected from other attached tissues in ice-cold KRB solution and transferred to KRB at room temperature before mounting them onto MCC Sylgard platforms Tracheas with intact cartilage were dissected from other attached tissues in ice-cold KRB solution and transferred to KRB at room temperature before mounting them onto MCC Sylgard platforms (Fig. 1 and Supplementary Figure S. 1)

Results

Discussion

Conclusion